A krypton atom ($Z = 36$) is in its ground state, $1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^{10}\,4s^2\,4p^6$. Each of its electrons has four quantum numbers $n$, $l$, $m_l$ and $m_s$. Which of the following statements about the electrons of this atom are correct?